The disclosure relates to a hydrostatic traction drive according to the description below and a vehicle with such a hydrostatic traction drive.
Such hydrostatic traction drives can generally be used in vehicles, in particular however in agricultural utility vehicles such as tractors.
DE 10 2006 058 802 A1 discloses a hydrostatic traction drive in which several hydromotors are supplied with pressure medium via a common variable pump. In the simplest case one hydromotor is allocated to the front axle and one hydromotor to the rear axle, so that on supply of pressure medium to both hydromotors (axle motors), the front and rear axles are driven. In a more complex embodiment example one hydromotor (wheel motor) is allocated to each wheel of the front and rear axles, of which motors again two are connected in series so that on all-wheel drive, the left or right wheels are driven via two hydromotors connected in series.
In the pressure medium flow path between the two hydromotors connected in series, a switch valve is arranged which is pre-tensioned in an open position in which a bypass line is opened, via which the pressure medium flows back from the outlet from the upstream hydromotor, bypassing the downstream hydromotor, to the low-pressure side of the traction drive, so that accordingly only the axle allocated to the upstream hydromotor is driven while the downstream hydromotor is effectively idling as it is being “carried” by the vehicle. To switch this two-wheel drive to four-wheel drive, the switch valve is brought into a blocked position in which the bypass line to the low pressure is blocked so the second hydromotor is also supplied with pressure medium. Switching from two-wheel to four-wheel drive in this solution is voluntary and depends on the experience of the driver.
DE 196 48 706 C2 discloses a hydrostatic traction drive with two hydromotors, each allocated to a wheel of a vehicle axle. In this hydrostatic traction drive a valve device is provided via which the two hydromotors can be connected in series or in parallel. When connected in parallel, the two hydromotors are exposed to practically the same pressure difference so that on cornering, an internal balancing of the through-flow quantities of the two hydromotors results. When connected in series, on cornering cavitations can occur due to the different rotation speeds, in series connection however a synchronous running of the two hydromotors is rather guaranteed.
It is furthermore known from the prior art that the traction drives described above have an articulated steering. With this system two axles of a vehicle are connected via an articulated joint and can pivot relative to each other, for example via hydraulic cylinders. Two wheels are allocated to each axle and can each can be driven by one hydromotor. Hydraulically the traction drive can be configured in particular according to DE 10 2006 058 802 A1. On a steering movement of the articulated steering i.e. on pivoting of the axles relative to each other, two wheels on one side of the vehicle with articulated steering move towards each other while two wheels on the other side move apart. The wheels of the respective side and hence the hydromotors of the respective series are exposed to opposing torques by the steering movement. Due to the opposing torques, the pressure in the pressure medium flow path between the hydromotors arranged in series and allocated to the wheels moving towards each other rises, while the pressure in the pressure medium flow path between the hydromotors of the other series falls. This pressure difference on a steering movement, in particular in the driving state of a vehicle fitted with hydrostatic traction drive, disadvantageously leads to different traction levels of the wheels.
In this context the object of the disclosure is to create a hydrostatic traction drive and a vehicle with such traction drive which eliminates said disadvantages.
This object is achieved by a hydrostatic traction drive with the features described below and by a vehicle with the features described below.
Other advantageous refinements of the disclosure are the subject of further description below.